Temperature regulator



Dec. 4, '1928. 1,694,264 A. w. HULL TEMPERATURE REGULATOR Filed June 22, 1925 2 Sheets-Sheet J Inventor: Alber't W. Hul I, b9 )t wz H Ls Atto neg.

Dec. 4, 1928. 1,694,264

A. w. HU LL TEMPERATURE REGULATOR Filed June 22, 1925 2 Sheets-Sheet 2 Tn ventor: Albert W.HUH,'

b9 H'Ls Attorney.

Patented Dec. 4, 1928.

UNITED STATES PA'raur err-E.

ALBERT W. HULL, OF SCHTENECTADY, NEW YORK, ASSIGNORJ TO GENERAL 7 1 COMPANY, A CORPORATION OF NEW YORK.

ELECTRIC TEMPERATURE REGULATOR.

11- Application filed June 22', 1925. Serial No. 38,842.

My invention relates to temperature regulators and has for its object the provision of simpleand reliable means for maintaining a predetermined temperature with precision.

More specifically my invention relates to temperature regulating apparatus for furnaces, ovens and the like, whereby a predeter mined temperature is automatically maintainedf My invention has particular application in the regulation of electrically heated devices.

In carrying out my invention I control the temperature of the heated device by means of an electron discharge device or tube having its output circuit energized from an alternating current source of supply, and its input circuit controlled by means responsive to the temperature of the heated device whereby the current in the plate circuit of r the electron discharge device is varied in such manner as to control the temperature. For a more complete understanding of my invention reference should be had to the accompanying drawing in which Fig. 1 is a diagrammatic representation of a temperature regulator embodying my invention, while Figs. 2 and 3 are views showing modified forms of my invention. 1

Referring to the drawing, I have shown my invention in one form as applied to an electric oven or furnace 10 which is heated by means of a resistor 11 connected to a suit able electrical supply source12. The temperature of the heated device 10 may be controlled by means of a switch 13 which when closed short circuits a section 11 of the resistor whereby the rate of heat generation is increased. As shown, this switch is normally in open position and may be raised to closed position by means of a mag net coil 14. For suitably controlling the 15 and an electron discharge device lti.

The IVheat-stone bridge comprises the usual four resistances17, 18, 19 and 20, the resistance 20 having a positive temperature coeflicient and being situated in the heated device 10 so as to be subjected to the temperature ,to be regulated. The bridge is energized from a suitable alternating current supply source 21, which may be the same as the voltage across the terminals 27 and 28 of the bridge. As shown, a step-up transformer 29 is used for the purpose of increasing the voltage applied to the grid circuit. In order to give the grid'a slight negative bias one terminal of the secondary of the transformer 29 is connected to the terminal 22 of the bridge while its other terminal is connected through a conductor 30 to the grid 25. The grid circuit is completed by means of a conductor 31 leading from the lament 24 to an intermediate point 32 of the resistance 18. It will be observed that with these connections for the grid circuit, when the plate is positive a negative bias will be introduced by the voltage drop across the portion of the resistance 18 between the terminal 22 and the point 32. The plate 26 of the tube is connected by means of a conductor 33 through the magnet coil 14 to one side of the supply source 21. The plate circuit is completed from the filament 24 to the supply source 21 through the conductor 31 to point 32, thence through. a portion of the resistance 18 to the terminal 22, and from the terminal 22 to the opposite side of the supply source 21. A suitable source of alternating current supply, which may be the supply source 21, is used for the filament 24, the connections being made through a transformer 24*.

The relative values of the resistances 17, 18, 19 and 20 are adjusted in such manner that upon the occurrence of a temperature in the heated device 10 which is slightly above a predetermined meantemperature'to be maintained," the potential of the terminal minal 28 when the terminal 23, and hence the plate 26, is positive, to such a degree that the transformer 29 will apply a negative potential to the grid suflicient to reduce the plate current to such a value that the magnet coil will release the switch 13 and allow it to open. This inserts section 11 of the 27 will be negative with respect to the terheating resistor in the heating circuit whereby the rate of generation of heat is reduced to such an extent that the temperature of the device 10 will tend to fall. It will be understood, of course, that the resistance 20 is exposed either to the full temperature oi the heated device 10 or in such manner as to be responsive to changes in the temperature of the device. Under the temperature conditions assumed, the resistance of resistance 20 will be increased by the increase in temperature to which it is exposed to a value sufiiciently greater than the resistance 19 to give the required difference in potential between the terminals 27 and 28 to operate the electron discharge device as previously described.

As the temperature of the device 10 now falls, the resistance 20 will decrease in value.

This results in a decrease in the difference of potential between the terminals 27 and 28 whereby the negative gTrid potential is correspondingly reduced. ventually when the resistance 20 has the same value as the resistance 19 the grid potential will be normal, that is, no potential will be impressed upon it by the transformer 29, and upon a further fall in temperature the potential of the terminal 27 will become positive with respect to the terminal 28 when the terminal 23 is positive. This action re sults in a gradually increasing flow. of current in the plate circuit in response to the falling temperature of the device 10 whereby the energization of the coil 14 is increased,

' and finally upon the occurrence of a predetermined minimum temperature, which is slightly below the temperature to be maintained, the energization of the coil 14 will be great enough to close the switch 13 and of the heating resistor. The temperature of the device 10 now rises and upon the occurrence of the predetermined maximum temperature devices may be used the cycle will be repeated as previously described. In this manner a predetermined mean temperature will be maintained.

By suitably adjusting the resistances of the bridge and the ratio of transformation of the step-up transformer 29, the apparatus may be arranged to give very close temperature regulation, for example it is entirely practicable to maintain a predetermined mean temperature to within plus or minus one-tenth of one degree Furthermore, to increase the sensitivity of the apparatus one or more additional electron as amplifiers.

In the modified form of my invention shown in Fig. 2, two stages of amplification are used. Each stage is shown as consisting of two electron discharge devices or tubes which are connected in ,a ptlsh-andpull or two wave circuit. One tube only may be used for each stage of amplification,

however. The terminals 27 and 28 are connected to the primary 35 of a transformer, the secondary 36 of which has its terminals connected to the grids of the amplifying devices 37 and 38, shown as being of the 3-electrode type. The secondary'36 is. provided with a central tap 39 whereby onehalf of the secondary is connected in the input or grid circuit of the tube 37, while the otherhalf is connected in the grid circuit of the tube 38. The plates of the tubes 37 and 38 are connected to the terminals of the primary 40 of a transformer, the secondary 41 of which has its terminals. connected to the grids of another pair of amplifying tubes 42 and 43. A central tap is provided on the primary coil 40 whereby one-half of the coil is connected in the output circuit of the tube 37, while the other half is connected in the output circuit of the tube 38,- a plate battery 44 being included in the tap connection. The connections for the tubes 42 and 43 are the same as the connections for F'th'e tubes 37 and 38 the output circuit of these tubes energizing the two halves of a primary coil 45 of a transformer, the secondary 46 of which has its terminals connected to the grids of two tubes 47 and 48 which also operate in pushand-pull circuits. The plate or output circuits of the tubes 47 and 48 are energized from the source of alternating current 21, preferably through a transformer 49. The secondary 50 of the transformer 49 has its terminals connected to the plates of the tubes 47 and; 48 and is provided with a central tap from which a conductor 51 leads through the magnet coil 14 to the filaments of the tubes. In this manner the output circuits of the tubes are energized by the halves of the secondary 50 respectively), the coil 14 being in the output circuits of 0th tubes, and therefore, rece ving a substantially true direct current.

The operation of this modification of my invention is substantially the same as the operation of the arrangement shown in Fig. 1 with the fundamental diiference that the coil 14 is energized with a substantially direct current. As with the apparatus of Fig. 1, the arrangement is such that negative potentials are applied to the grids of the tubes 47 and 48 when their plates are positive upon the occurrence of the predetermined maximum temperature. Likewise a positive potential is applied to the grids of the tubes when their plates are positive upon the occurrence of a predetermined minimum temperature. It may be desirable'to use two stages of amplification, as shown, in order to obtain the correct phase relations. due to the fact that with transformer coupling between the tubes, the currents in the output circuits of electron discharge devices are considerably out of phase with those in too This is the input circuits. Where two stages of amplification are used a phase difference of substantially 180 is introduced by the tubes which is taken into account in selecting the polarity of the connections. If resistance and condenser coupling between the tubes is used the plate voltage of each tube is exactly 180 out of phase with the grid voltage, and one or any desired number of stages of amplification may be used.

In the modified form of my invention shown in Fig. 3, I have utilized a vapor electric electron discharge device for con.- trolling the supply of electric current to the furnace. This vapor electron discharge device has sufficient capacity to carry the total amount of current required for the furnace so that no relays are necessary. The device is provided with two plates or anodes 56 and 57, grids 58 and 59, and with a central cathode 60 consisting of a small quantity of mercury. An exciting battery .61 is provided and a switch 62 whereby by closing the switch 62 the cathode is excited in a Well known manner. Preferably the switch 62 remains closed during the operation of the furnace. This device functions as a twoway rectifier. When a positive voltage is applied to one of the plates 56 and 57 an arc is formed between this plate and the cathode 60, but when this plate becomes negative the arc is extinguished. The function of the grids is to control the formation of the arcsu \Vhen the potentials of the. grids are lower than a predetermined value the arcs will not start and when the grid potentials are above this value the arc will start. The characteristics of the device 55 may be such that certain negative grid potentials will prevent, operation, while certain positive grid potentials will produce operation.

In this modification of my invention the electrical connections between the VVheatstone bridge 63 and the alternating current source of supply 64 are substantially the same as shown in Figs. 1 and 2, one leg 65 of the bridge being in the furnace 66. The heating resistor 67 for the furnace has one terminal connected by Way of the conductor 68 to a central point on the secondary 69 of the transformer 70, the primary of which is connected across the supply source 64. The remaining terminal of the resistor is connected through a conductor 71 'to the cathode 60. The terminals of the secondary 69 are connected to the plates 56 and 57. It will thus be observed that the resistor 67 is connected in circuit with the rectifying dc.- vice 55, which is energized from the trans-. former 70, so as to be supplied with a pulsating direct current when the device is in operation.

The energization of the grids58 and 59 is controlled by means of the bridge 63, 'two 3- electrode electron discharge devices or tubes 72 and 73 beingprovided for purposes of amplification. The input circuits of the tubes areaconnected to the points 74 and 75 ol" the bridge. which correspond with the points 27 and 28 of Figs. 1 and 2, by means of atransformer 76 having two secondaries '77 and 78 connected in the input circuits of the tubes 72 and 73 respectively. Any suitable source of alternating or direct current may be used for heating the filaments of the tubes. As shown, the filaments are heated by means of alternating current which may be derived from the supply source 64:, the connection with the filaments being made through suitable transformers 79 and 80.

As shown, the energization for the output circuits of the tubes is obtained from the transformer 70, the plate of the tube 72 being connected to oneterminal of the second ary 69 through a conductor 81 while the plate of the tube 73 is connected to the other .terminal of the secondary 69 bymeans of a conductor 82. Two resistances 83 and 84 are provided each having one terminal connected to the cathode 60 through a battery 85, while the remaining terminals are connected to the cathodes or filaments of the tubes 72 and 73, respectively, and also through conductors 86 and 87 to the grids 58 and 59.

It will thus be observed that the output circuit of the tube 72 leads from its plate through the conductor 81 to the left hand terminal of the secondary 69, through the left hand half of the secondary, and thence through conductor 68, the resistor 67, conductor 71, battery and resistance 83 to the filament of tube 72. In a similar manner the output circuit of the tube 73 is completed through the right hand half of the secondary 69 and the resistance 84. The battery 85 is connected so as to apply a negative potential to the grids 58 and 59 when the tubes 72 and 73 are not in operation and thus prevent operation of the device 55 when the tubes 72 and 73 are not in operation. This battery 85 is not indispensable although its use is preferable. When the tubes 72 and 73 are in operation, the currents in their plate circuits produce voltage drops across the resistances 83 and 84: which voltage drops are opposed to and greater than the potential of the battery 85, the differences being applied to the grids 58 and 59 whereby the grids are. made positive and the vapor electric device 55 set in operation.

The arrangement is such that when the the primary of transformer 7 O is positive the left-hand side of secondary 69 and hence the plate to the tube 7 2 will be positive. Under these conditions also, the point 74 will be negative with respect-to the point 7 5, and

consequently the grid of the tube 73 positive, when the plate of the tube 73 is positive since the polarities in transformers 70 and 7 6 will then be reversed. Therefore, when the furnace is at this low temperature the tubes 7 2 and 73 will operate, and the arrangement is such that positive voltages due to the drops across the resistances 83 and 84 will be applied to the grids 58 and 59 when the plates 56 and 57 are respectively positire. The device thus operates to supply full load current to the heating'resistor 67 until such time as the temperature rises to some predetermined maximum value above the mean temperature, under. which condition the point 74c will be negative with respect to point 75 and consequently the tubes 79. and 73 will be prevented from operating. inder these conditions the battery 85 applies negative voltages to the grids 58 and 59 whereby the device 55 is prevented from operating. As a result no current is supplied to the resistor 67 by the device 55 and the temperature of the furnace therefore falls until upon the occurrence of the predetermined minimum temperature previously assumed, the device 55 will be set in operation, the cycle of operation being repeated aspreviously described. 7

If less exact regulation is desired the amplifier tubes 72 and 7 3 may be omitted and one of the terminals of each of the secondaries 77 and 78 connected directly to the grids 58 and 59 respectively of the device 55, the other terminals of the secondaries being connected directly to the cathode 60.

lVhile I have described my invention as embodied inconcrete form and as operating in a specific manner in accordance with the provisions of the patent statutes, it should be understood that I do not limit my invention thereto, since various modifications thereof will suggest themselves to those skilled in the art without departing from the spirit of my invention, the scope of which is set forth in the annexed claims.

What I claim as new and desire to secure by Letters Patent of the United States is 1. A temperature regulator comprising temperature responsive means for causing an electromotive force to be produced increasing from zero in one direction when the temperature rises above a predetermined the left-hand sides of the secmean temperature and from zero 'in the opposite direction when the temperature falls below said predetermined mean temerature', and temperature control means responsive to said electromotive force.

2. In a temperature regulator, the combination with a heated device, of heating means therefor, a Wheatstone bridge havin a resistance'var in with the tem erature of said heated device, a source of electrijcal supply for said bridge whereby said bridge causes an electromotive force to be tromotive force to be applied to said input circuit varying 1n polarity in accordance with said temperature whereby the current in the output circuit of said device is varied. and means responsive to the current in said output circuit for controlling said temperature.

' i. A temperature regulator comprising an electron discharge device provided with a grid and a plate, means responsive to the temperature to be regulated for causing a positive or a negative potential to be applied to said grid in accordance with the degree of said temperature, a source of alternating current supply in the plate circuit of said device, and temperature control means responsive to the current in said plate circuit.

5. A temperature regulator comprising a Wheatstone bridge provided with a resistance varying with the temperature to be regulated, an electron discharge device having input and output circuits, connections between the input circuit of said discharge device and said bridge, said bridge being arranged to apply an electromotive force to said input circuit varying in accordance with the temperature to be regulated. and temperature control means responsive to the current in the output circuit of said discharge device.

6. A temperature regulator comprising an electron discharge device provided with input and output circuits, a source of alternating current supply for the output circuit of said device, temperature control means connected in said output circuit, and temperature responsive means for controlling the energization of the input circuit of said device so as to vary the current in said output circuit, whereby said temperature controhmeans is operated to maintain a: predetermined temperature.

7. A temperature regulator comprising an electron discharge device rovided with a grid and a plate, a source 0 alternating current supply for the plate circuit of said device, temperature responsive means for causing a negative potential to be applied to said grid when said plate is positive upon the occurrence of a predetermined temperature and for causing a positive potential to be applied to said grid when said plate is positive upon the occurrence of a predetermined different temperature, and temperature control means-responsive to the current in said plate circuit.

8. A regulating VVheatstone bridge having a resistance varying with the quantity to be regulated, a source of alternating current supply for said bridge, an electron discharge device controlled by the unbalance of said bridge, connections between the output circuit of said discharge device and said supply source, and controlling means responsive to the current in said output circuit.

9. A temperature regulator comprising a \Vheatstone bridge provided with a resistance varying with the temperature to be regulated, a source of alternating current supply connected across two of the terminals of said bridge, an electron discharge device provided with input and output circuits, connections between said input circuit and the other two terminals of said bridge, connections between said output circuit and said supply source, and temperature control means in said output circuit responsiveto the current in said output circuit so as to maintain a predetermined temperature.

10. In a temperature regulator, the combination with a heated device, electric heating means therefor, a source of electrical supply for said heater, an electron'discharge device having its output circuit connected to said supply source in series with said heating means, and means responsive to the temperature of said heated device for controlling said electron discharge device in such manner that the supply of electrical energy to said heating means is interrupted upon the occurrence of a predetermined tem perature. p

11. In a temperature regulator, the combination with a heated device, of a Wheatstone bridge having a resistance varying with the temperature of said heated device, a source of alternating current supply for said bridge, and electron discharge device controlled by said bridge, electrical connections between the output circuit of said discharge device andsaid supply source, and a heating resistor for said heated device connected in said output circuit.

and a grid for controllin device com risin a 12. In a temperature regulator, the combination with a heated device, of electric heating means'therefor, a source of alternating current supply for said heater, an electron-discha'rge'device provided with a plate the supply of electrical energy from said supply source to said heated device, electrical connections between said supply source and the plate circuit of said discharge device, and means responsive to the temperature of said heated device for causing a negative potential to be applied to the grid of said discharge device when said plate is positive upon the occurrence of a predetermined maximum temperature whereby the supply of energy to said heating means is cut off.

13. In a temperature regulator, the combination with a heated device, of electric heating means therefor, a source of alternating current supply for said heater, an electron discharge device provided with a plate and a grid for controlling the supply of electrical energy from said supply source to said heated device, a Wheatstone bridge having one resistance responsive to the temperature of said heated device, electrical connections between said supply source and said bridge, and means for applying the unbalance voltage of said bridge to the grid of said electron discharge device in such manner that upon the occurrence of a predetermined maximum temperature said grid is negative when said plate is positive whereby the supply of electrical energy to said heating means is cut off.

'14. In a temperature regulator, the combination with a heated device, a VVheatstone bridge having one resistance responsive to the temperature of said heated device, a source of alternating current supply, electrical connections between said supply source and said bridge, an electron discharge device provided with a grid and a plate, means for applying the unbalance voltage of said bridge to the grid circuit electron discharge device, electrical connections between the output circuit of said dis charge device and said supply source, and a heating resistor for said heated device connected in said output circuit, said connections being so arranged that upon the occur rence of a predetermined minimum temperature a positive potential is applied to said grid when said plate is positive whereby a heating current is produced in said resistor.

15. In a temperature regulator, the combination with a heated device, of a heating resistor therefor, a source of alternating current for said resistor, a Wheatstone bridge having one resistance responsive to the temperature of said heated device, electrical connections between said bridge and said supply source, a vapor electric device provided with a cathode, two anodes, and two of said grids, a transformer connected to said supply source having its secondary connected to said anodes, a connection including said resistor between a central point of said secondary and said cathode, a pair of three-electrode electron tubes for amplifying the unbalance voltage of said bridge, electrical connections between said Whez tstone bridge and the input circuits of said tubes, electrical connections between the plates of said tubes and said secondary, electrical connections between the filaments of said tubes and said grids, and electrical connections including resistances between the filaments of said tubes and said cathode, said connections being so arranged that said vapor electric device is controlled in response to the unbalance voltage of said bridge to supply current to said resistor so as to maintain a. predetermined temperature.

16. A temperature regulator comprising an electron discharge deviceprovided with input and output circuits, means responsiveto the temperature to be regulated for causing an electromotive force varying in polarity in accordance with said temperature to be applied to said input circuit, a source of alternating current supply for said output circuit, and temperature control means responsive to the electromotive force in said output circuit.

17 A temperature regulator comprising a Wheatstone bridge, an electrical supply source for said bridge, an electron discharge device, connections between the output circuit of said discharge device and said supply source, said connections including a control device responsive to the current in said output circuit, and means including a resistance of said bridge responsive to the temperature to be controlled for causing a potential varying in polarity to be applied to the input circuit of said discharge device.

In witness whereof I have hereunto set my 'hand this 19th day of June, 1925.

ALBERT W. HULL. 

